Database System Concepts, 5th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 1: Introduction
Chapter 1: Introduction
©Silberschatz, Korth and Sudarshan1.2Database System Concepts - 5th Edition, Sep 6, 2006
Chapter 1: Introduction
Chapter 1: Introduction
Purpose of Database Systems
View of Data
Database Languages
Relational Databases
Database Design
Object-based and semistructured databases
Data Storage and Querying
Transaction Management
Database Architecture
Database Users and Administrators
Overall Structure
History of Database Systems
©Silberschatz, Korth and Sudarshan1.3Database System Concepts - 5th Edition, Sep 6, 2006
Database Management System (DBMS)
Database Management System (DBMS)
DBMS contains information about a particular enterprise
zCollection of interrelated data
zSet of programs to access the data
zAn environment that is both convenient and efficient to use
Database Applications:
zBanking: all transactions
zAirlines: reservations, schedules
zUniversities: registration, grades
zSales: customers, products, purchases
zOnline retailers: order tracking, customized recommendations
zManufacturing: production, inventory, orders, supply chain
zHuman resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives
©Silberschatz, Korth and Sudarshan1.4Database System Concepts - 5th Edition, Sep 6, 2006
Purpose of Database Systems
Purpose of Database Systems
In the early days, database applications were built directly on top of
file systems
Drawbacks of using file systems to store data:
zData redundancy and inconsistency
Multiple file formats, duplication of information in different files
zDifficulty in accessing data
Need to write a new program to carry out each new task
zData isolation — multiple files and formats
zIntegrity problems
Integrity constraints (e.g. account balance > 0) become
“buried” in program code rather than being stated explicitly
Hard to add new constraints or change existing ones
©Silberschatz, Korth and Sudarshan1.5Database System Concepts - 5th Edition, Sep 6, 2006
Purpose of Database Systems (Cont.)
Purpose of Database Systems (Cont.)
Drawbacks of using file systems (cont.)
zAtomicity of updates
Failures may leave database in an inconsistent state with partial
updates carried out
Example: Transfer of funds from one account to another should
either complete or not happen at all
zConcurrent access by multiple users
Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
Example: Two people reading a balance and updating it at the
same time
zSecurity problems
Hard to provide user access to some, but not all, data
Database systems offer solutions to all the above problems
©Silberschatz, Korth and Sudarshan1.6Database System Concepts - 5th Edition, Sep 6, 2006
Levels of Abstraction
Levels of Abstraction
Physical level: describes how a record (e.g., customer) is stored.
Logical level: describes data stored in database, and the relationships
among the data.
type customer = record
customer_id : string;
customer_name : string;
customer_street : string;
customer_city : integer;
end
View level: A way to hide: (a) details of data types and (b) information
(such as an employee’s salary) for security purposes.
©Silberschatz, Korth and Sudarshan1.7Database System Concepts - 5th Edition, Sep 6, 2006
View of Data
View of Data
An architecture for a database system
©Silberschatz, Korth and Sudarshan1.8Database System Concepts - 5th Edition, Sep 6, 2006
Instances and Schemas
Instances and Schemas
Similar to types and variables in programming languages
Schema the logical structure of the database
zExample: The database consists of information about a set of customers and
accounts and the relationship between them)
zAnalogous to type information of a variable in a program
zPhysical schema: database design at the physical level
zLogical schema: database design at the logical level
Instance the actual content of the database at a particular point in time
zAnalogous to the value of a variable
Physical Data Independence the ability to modify the physical schema without
changing the logical schema
zApplications depend on the logical schema
zIn general, the interfaces between the various levels and components should
be well defined so that changes in some parts do not seriously influence others.
©Silberschatz, Korth and Sudarshan1.9Database System Concepts - 5th Edition, Sep 6, 2006
Data Models
Data Models
A collection of tools for describing
zData
zData relationships
zData semantics
zData constraints
Relational model
Entity-Relationship data model (mainly for database design)
Object-based data models (Object-oriented and Object-relational)
Semistructured data model (XML)
Other older models:
zNetwork model
zHierarchical model
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Data Manipulation Language (DML)
Data Manipulation Language (DML)
Language for accessing and manipulating the data organized by the
appropriate data model
zDML also known as query language
Two classes of languages
zProcedural user specifies what data is required and how to get
those data
zDeclarative (nonprocedural) user specifies what data is
required without specifying how to get those data
SQL is the most widely used query language
©Silberschatz, Korth and Sudarshan1.11Database System Concepts - 5th Edition, Sep 6, 2006
Data Definition Language (DDL)
Data Definition Language (DDL)
Specification notation for defining the database schema
Example: create table account (
account-number char(10),
balance integer)
DDL compiler generates a set of tables stored in a data dictionary
Data dictionary contains metadata (i.e., data about data)
zDatabase schema
zIntegrity constraints
Domain constraints
Referential integrity (references constraint in SQL)
Assertions
zAuthorization
Data storage and definition language
zSpecifies the storage structure and access methods used
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Relational Databases
Relational Databases
A relational database is based on the relational data model
Data and relationships among the data is represented by a
collection of tables
Includes both a DML and a DDL
Most commercial relational database systems employ the SQL
query langue.
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Relational Model
Relational Model
Example of tabular data in the relational model
Attributes
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A Sample Relational Database
A Sample Relational Database
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SQL
SQL
SQL: widely used non-procedural language
zExample: Find the name of the customer with customer-id 192-83-7465
select customer.customer_name
from customer
where customer.customer_id = ‘192-83-7465’
zExample: Find the balances of all accounts held by the customer with
customer-id 192-83-7465
select account.balance
from depositor, account
where depositor.customer_id = ‘192-83-7465’ and
depositor.account_number = account.account_number
Application programs generally access databases through one of
zLanguage extensions to allow embedded SQL
zApplication program interface (e.g., ODBC/JDBC) which allow SQL
queries to be sent to a database
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Database Design
Database Design
The process of designing the general structure of the database:
Logical Design – Deciding on the database schema. Database design
requires that we find a “good” collection of relation schemas.
zBusiness decision – What attributes should we record in the
database?
zComputer Science decision – What relation schemas should we
have and how should the attributes be distributed among the various
relation schemas?
Physical Design – Deciding on the physical layout of the database
©Silberschatz, Korth and Sudarshan1.17Database System Concepts - 5th Edition, Sep 6, 2006
The Entity
The Entity-
-Relationship Model
Relationship Model
Models an enterprise as a collection of entities and relationships
zEntity: a “thing” or “object” in the enterprise that is distinguishable
from other objects
Described by a set of attributes
zRelationship: an association among several entities
Represented diagrammatically by an entity-relationship diagram:
©Silberschatz, Korth and Sudarshan1.18Database System Concepts - 5th Edition, Sep 6, 2006
Object
Object-
-Relational Data Models
Relational Data Models
Extend the relational data model by including object orientation and
constructs to deal with added data types.
Allow attributes of tuples to have complex types, including non-atomic
values such as nested relations.
Preserve relational foundations, in particular the declarative access to
data, while extending modeling power.
Provide upward compatibility with existing relational languages.
©Silberschatz, Korth and Sudarshan1.19Database System Concepts - 5th Edition, Sep 6, 2006
XML: Extensible Markup Language
XML: Extensible Markup Language
Defined by the WWW Consortium (W3C)
Originally intended as a document markup language not a
database language
The ability to specify new tags, and to create nested tag structures
made XML a great way to exchange data, not just documents
XML has become the basis for all new generation data interchange
formats.
A wide variety of tools is available for parsing, browsing and
querying XML documents/data
©Silberschatz, Korth and Sudarshan1.20Database System Concepts - 5th Edition, Sep 6, 2006
Storage Management
Storage Management
Storage manager is a program module that provides the interface
between the low-level data stored in the database and the application
programs and queries submitted to the system.
The storage manager is responsible to the following tasks:
zInteraction with the file manager
zEfficient storing, retrieving and updating of data
Issues:
zStorage access
zFile organization
zIndexing and hashing
©Silberschatz, Korth and Sudarshan1.21Database System Concepts - 5th Edition, Sep 6, 2006
Query Processing
Query Processing
1. Parsing and translation
2. Optimization
3. Evaluation
©Silberschatz, Korth and Sudarshan1.22Database System Concepts - 5th Edition, Sep 6, 2006
Query Processing (Cont.)
Query Processing (Cont.)
Alternative ways of evaluating a given query
zEquivalent expressions
zDifferent algorithms for each operation
Cost difference between a good and a bad way of evaluating a query can
be enormous
Need to estimate the cost of operations
zDepends critically on statistical information about relations which the
database must maintain
zNeed to estimate statistics for intermediate results to compute cost of
complex expressions
©Silberschatz, Korth and Sudarshan1.23Database System Concepts - 5th Edition, Sep 6, 2006
Transaction Management
Transaction Management
A transaction is a collection of operations that performs a single
logical function in a database application
Transaction-management component ensures that the database
remains in a consistent (correct) state despite system failures (e.g.,
power failures and operating system crashes) and transaction failures.
Concurrency-control manager controls the interaction among the
concurrent transactions, to ensure the consistency of the database.
©Silberschatz, Korth and Sudarshan1.24Database System Concepts - 5th Edition, Sep 6, 2006
Database Architecture
Database Architecture
The architecture of a database systems is greatly influenced by
the underlying computer system on which the database is running:
Centralized
Client-server
Parallel (multi-processor)
Distributed
©Silberschatz, Korth and Sudarshan1.25Database System Concepts - 5th Edition, Sep 6, 2006
Database Users
Database Users
Users are differentiated by the way they expect to interact with
the system
Application programmers interact with system through DML calls
Sophisticated users form requests in a database query language
Specialized users write specialized database applications that do
not fit into the traditional data processing framework
Naïve users invoke one of the permanent application programs that
have been written previously
zExamples, people accessing database over the web, bank tellers,
clerical staff
©Silberschatz, Korth and Sudarshan1.26Database System Concepts - 5th Edition, Sep 6, 2006
Database Administrator
Database Administrator
Coordinates all the activities of the database system; the
database administrator has a good understanding of the
enterprise’s information resources and needs.
Database administrator's duties include:
zSchema definition
zStorage structure and access method definition
zSchema and physical organization modification
zGranting user authority to access the database
zSpecifying integrity constraints
zActing as liaison with users
zMonitoring performance and responding to changes in
requirements
©Silberschatz, Korth and Sudarshan1.27Database System Concepts - 5th Edition, Sep 6, 2006
Overall System Structure
Overall System Structure
©Silberschatz, Korth and Sudarshan1.28Database System Concepts - 5th Edition, Sep 6, 2006
History of Database Systems
History of Database Systems
1950s and early 1960s:
zData processing using magnetic tapes for storage
Tapes provide only sequential access
zPunched cards for input
Late 1960s and 1970s:
zHard disks allow direct access to data
zNetwork and hierarchical data models in widespread use
zTed Codd defines the relational data model
Would win the ACM Turing Award for this work
IBM Research begins System R prototype
UC Berkeley begins Ingres prototype
zHigh-performance (for the era) transaction processing
©Silberschatz, Korth and Sudarshan1.29Database System Concepts - 5th Edition, Sep 6, 2006
History (cont.)
History (cont.)
1980s:
zResearch relational prototypes evolve into commercial systems
SQL becomes industrial standard
zParallel and distributed database systems
zObject-oriented database systems
1990s:
zLarge decision support and data-mining applications
zLarge multi-terabyte data warehouses
zEmergence of Web commerce
2000s:
zXML and XQuery standards
zAutomated database administration
Database System Concepts, 5th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
End of Chapter 1
End of Chapter 1
©Silberschatz, Korth and Sudarshan1.31Database System Concepts - 5th Edition, Sep 6, 2006
Figure 1.4
Figure 1.4
©Silberschatz, Korth and Sudarshan1.32Database System Concepts - 5th Edition, Sep 6, 2006
Figure 1.7
Figure 1.7